Unhappy Car Service City client

I have sent a car for service and after three days it never started. When I towed it back to them, they fixed it after three weeks and I paid R 8 500.00. When I was driving it back home it gave me the engine light (to show that it is faulty). I drove back in the morning and told them that it is giving me Engine light. They took it back and was not fixed for three months. Now, today (23 January 2019) being taken in on the 29th of October 2018 they are telling me that they cannot fix it. It is something different. When they fixed it for the first time they were just assuming that whatever they have done might be the problem. So, I paid R 8 500.00 for assumption. Now I have to go fetch the car or pay R 20 000.00 for them to fix the Injectors. I am very unhappy because I don't have the R 20 000.00 and I use the car for my business and I couldn't work for 3 months because I had no car.